1. Field of the Invention
The present invention relates to a pressure accumulation fuel injection controller used mainly in a diesel engine.
2. Description of Related Art
A pressure accumulation fuel injection device having a pressure accumulation vessel (common rail), a fuel injection valve (injector) and a suction metering fuel supply pump is known as a fuel injection device for a diesel engine. The pressure accumulation vessel accumulates high-pressure fuel according to a fuel injection pressure. The injector injects and supplies the high-pressure fuel in the accumulation vessel into each cylinder of the engine. The supply pump pressurizes the fuel suctioned into a pressurization chamber to high pressure and pressure-feeds the fuel to the pressure accumulation vessel.
Common rail pressure in the pressure accumulation vessel of the conventional pressure accumulation fuel injection device invariably fluctuates in a waveform because the common rail pressure receives pulsation of the fuel supply pump driven by the engine. In this case, a fuel injection amount differs depending on which point of the waveform of the pressure fluctuation coincides with the injection period of the fuel injection valve. The injection amount changes due to the fluctuation of the pressure during the injection. For example, the injection amount becomes large if the fuel injection is performed at a high point of the pressure fluctuation waveform. The injection amount becomes small if the fuel injection is performed at a low point of the pressure fluctuation waveform. Therefore, conventionally, the common rail pressure at the time when the fuel injection valve erupts the fuel is read in, and control for achieving the same injection amount is performed by regulating the injection period based on the fuel eruption pressure.
The fuel is atomized quite minutely if the eruption pressure is high when the control for achieving the same injection amount is performed. In this case, the fuel burns easily and cleanly so as to inhibit generation of smoke and to improve combustion efficiency. However, the fuel is not atomized well when the eruption pressure is low. In this case, the fuel is difficult to burn and the smoke can be generated easily, deteriorating the combustion efficiency. Accordingly, the combustion is not stabilized, so engine performance varies and is destabilized. The fuel supply pump may be controlled as a countermeasure. However, the control of the fuel supply pump is difficult because the fuel supply pump works with the engine.
JP-A-H11-148400 describes a pressure accumulation fuel injection device that has a pressure reduction valve (discharge valve) for releasing the pressure accumulation vessel to a lower pressure side. The fuel injection device opens the pressure reduction valve under a certain operation condition (for example, an acceleration operation resumed immediately after rapid deceleration of the engine or operation immediately after shift-up) in which the fuel pressure in the pressure accumulation vessel exceeds a target value. Thus, the fuel injection device avoids an excessive injection rate and inhibits diesel knocking or discharge of nitrogen oxides (NOx).
The fuel injection device of JP-A-H11-148400 functions as a failsafe device for handling an abnormality in a specific operation state such as acceleration resumed immediately after rapid deceleration or operation immediately after shift-up. However, this fuel injection device does not invariably control the pressure reduction valve. Therefore, problems of instable combustion of the engine and variation or instability of the engine performance still remain.